require 'logger'
module Gitlab
  module Metrics
    class BaseSampler < Daemon
      # interval - The sampling interval in seconds.
      def initialize(interval)
        interval_half = interval.to_f / 2

        @interval = interval
        @interval_steps = (-interval_half..interval_half).step(0.1).to_a

        super()
      end

      def safe_sample
        sample
      rescue => e
        Rails.logger.warn("#{self.class}: #{e}, stopping")
        stop
      end

      def sample
        raise NotImplementedError
      end

      # Returns the sleep interval with a random adjustment.
      #
      # The random adjustment is put in place to ensure we:
      #
      # 1. Don't generate samples at the exact same interval every time (thus
      #    potentially missing anything that happens in between samples).
      # 2. Don't sample data at the same interval two times in a row.
      def sleep_interval
        while (step = @interval_steps.sample)
          if step != @last_step
            @last_step = step

            return @interval + @last_step
          end
        end
      end

      private

      attr_reader :running

      def start_working
        @running = true
        sleep(sleep_interval)

        while running
          safe_sample

          sleep(sleep_interval)
        end
      end

      def stop_working
        @running = false
      end
    end
  end
end
